112 ON THE ANATOMY OP THE FLY. 



opening of the fifth abdominal segment. It consists of four 

 segments, the anterior three of which are separated by mem- 

 branous interspaces equal in length to the segments, and when 

 the organ is retracted each segment is withdrawn within the 

 next anterior to it, like the draw-tube of a telescope. The 

 posterior segment is attached closely to the penultimate, and, 

 like the ninth abdominal segment in the male, is considerably 

 modified, and bears a pair of leaf -like appendages which termi- 

 nate the rectum. 



The first and second segments of the ovipositor are like the abdominal 

 segments ; they consist of a dorsal and ventral plate, and have a fringe of 

 long vibrissas-like setae along their posterior margin. The third consists of 

 three plates, two of which are dorsal or lateral, and the third is ventral ; 

 it is slightly cleft posteriorly, and its extremity is covered with hairs. 



The fourth segment (Plate X., fig. 6) consists of a small triangular dorsal 

 plate which bears a pair of leaf -like lateral appendages covered with hairs. 

 These surround the dorsal part of the opening of the rectum. The intestine 

 is separated from the oviduct by a curved semicircular plate (Plate X., fig. 

 4), the angles of which are anterior and prolonged as apode"mes which 

 give insertion to a pair of muscle?, which arise from the ventral plate of 

 the third segment, and embrace the oviduct. Its curved border is posterior 

 and is fringed with hairs. It is probably the ventral plate of the last 

 abdominal segment ; if such is the case, the oviduct opens between the 

 last and penultimate segments of the ovipositor on its ventral aspect. 



The development of the sexual organs commences in the 

 larva, and so presents an exception to the other organs of the 

 imago. The ovaries or testes are found as a pair of cellular 

 bodies adhering together on the under side of the rectum, near 

 its termination. Dr. Weismann* figures both male and female 

 organs in this condition, and asserts that even at that early 

 period they present distinctive characters. I have been 

 unable to verify this assertion, although I believe it is likely 

 that Dr. Weismann is quite correct in this, as in most of his 

 elaborate researches. 



* Kolliker's Zeitschrift. Band XIV. 



